Here are my Expression Maps for using GPO5 with Dorico. The package includes: documentation of what I’ve done, so that you can understand it and adapt it to your needs; a spreadsheet of what switches and CCs various instrument groups use, and which Brass instruments use which maps.
There’s also a general-purpose Garritan Ex map, which should work (to some degree) for other Garritan libraries, such as the bundled Finale instruments.
Let me know how you get on, and if there are any egregious problems.
Version 2: fixed a minor issue.
GPO Archive.zip (82.3 KB)